Switching and interrupting devices such as fuses and circuit breakers are used in certain electrical systems for protecting an electrical circuit coupled to an electrical power supply. Such circuit breakers may be included within housings or cabinets along with other switching components. Switchgear and switchboard are general terms which are used to cover metal enclosures housing such switching and interrupting devices along with associated control, instrumentation, and metering devices. Such terms are also used to describe assemblies of these devices with associated buses, interconnections, and supporting structures used for distribution of electric power. Low voltage switchgear and switchboards operate at voltages up to 635 volts and with continuous electrical currents that may exceed 5000 amperes. They are generally designed to withstand short-circuit currents up to 200,000 amperes.
Typical switchgear equipment is an assembly composed of multiple metal enclosed sections. Each section may have several circuit breakers (e.g., stacked one above the other vertically in the front of the section) with each circuit breaker being enclosed in its own metal compartment. Each section may have a vertical or section bus which supplies current to the circuit breakers within the section via short horizontal branch buses that extend through insulated openings in the rear wall of the breaker compartments, for example. The vertical buses in each section may be supplied with current by a horizontal main bus that runs through the line-up. These connected busses make up the primary electrical circuit of the switchgear. There may also be a secondary electrical circuit used to control the breakers and other devices.
Typical switchgear requires individual circuit breakers to be manually connected and disconnected (racked in and out) from their electrical contacts. In prior systems, this may be accomplished by turning a racking handle which moves the circuit breaker into and out of the enclosed section. Extensive Personal Protective Equipment (PPE) is generally required for this operation, since the operator must stand directly in front of the gear to operate the circuit breaker.
Power circuit breakers have 3 positions: disconnected, test, and connected. For some power circuit breakers, the throw may be approximately 2 inches between the disconnected and connected positions. In the disconnected position, the circuit breaker is not in contact with a primary or secondary electrical circuit adapted to be protected by the breaker. This disconnected position may allow for the breaker to be removed from the switchgear for maintenance. In the test position, the breaker is in electrical contact with the secondary electrical circuit, but not the primary electrical circuit. This allows the circuit breaker to be opened and closed for testing the electrical control scheme of the switchgear, e.g. testing relays, circuit breaker coordination, etc. In the connected position, the circuit breaker may connect to both the primary and secondary circuits. This is the normal operating position.
Accordingly, there is a need for a circuit breaker system which may be safely racked into and out of the enclosure without the need to extensive PPE.